This is a Competitive Revision Application (notice number NOT-OD-09-058 and Notice Title: NIH Announces the Availability of Recovery Act Funds for Competitive Revision Applications), which is focused on broadening the scope of the parent grant, GM062942 entitled "Mechanism of Mitochondrial Fusion" to encompass the structural analysis of the fusion DRP, Mgm1. Mitochondria are dynamic, essential, double-membraned organelles that perform a myriad of tasks within cells. Unlike their bacterial ancestors, they are not discrete entities. Isolated mitochondria are transient and in communication via fusion to form both localized and widespread mitochondrial syncytia within cells. Mitochondrial division antagonizes fusion and together these events function to create a compartment that is connected, with access to mtDNA, and thus functional, yet able to be distributed to distant cellular destinations via transport on actin or microtubule networks. We are focused on understanding the molecular mechanism of mitochondrial fusion to gain insight into the roles and regulation of fusion in cells and disease. In addition to its fundamental cellular role, mitochondrial fusion also regulates intrinsic apoptosis in cells and conversely, the pro-apoptotic Bcl-2 proteins regulate mitochondrial fusion in healthy cells. The important cellular roles of fusion are underscored by the fact that mitochondrial fusion is required for embryonic development and mutations in fusion proteins cause neurodegenerative diseases and stroke. Mitochondrial fusion is unique in that it is mediated by the action of highly conserved dynamin-related proteins (DRPs). DRPs are large GTPases that, through their ability to self-assemble and hydrolyze GTP, control membrane remodeling events. Our powerful yeast in vitro assay has revealed a wealth of information regarding the fusion mechanism. We have demonstrated that DRPs mediate both membrane tethering and lipid-mixing steps in fusion at the mitochondrial outer and inner membranes. Our recent work also indicates that a non-DRP outer membrane fusion protein is required post-membrane tethering, at the lipid-mixing step of outer and inner membrane fusion. Information from the structural analysis of Mgm1 will provide novel insight into the molecular events of inner membrane fusion and guide the biochemical experiments proposed in the original grant. In addition, the structural analysis of assembled Mgm1 will provide invaluable insight in the general function, mechanism and properties of DRP family members. The funds provided by this grant will address the goals of the Recovery act by providing for the salary and training of a junior post-doctoral scientist. PUBLIC HEALTH RELEVANCE: Mitochondria perform many important roles in cells, including the production of energy. This critical mitochondrial function and others depend on mitochondrial fusion and defects in mitochondrial fusion in humans cause neurodegenerative diseases and stroke.